Field
Embodiments relate generally to the field of thermal decomposition and, more particularly but not exclusively, to retorts that are used in thermal decomposition.
Discussion of Related Field
Thermal decomposition is a process in which feedstock is heated to enable chemical reaction that results in breaking of the feedstock into multiple substances. In certain applications, catalyst may be used during thermal decomposition to reduce the temperature and pressure requirements of thermal decomposition and achieve desired results.
The concept of thermal and thermal-catalytic decomposition has been applied in various fields. One such field is recycling of waste feedstock, such as waste plastics to obtain original monomers, petroleum fuels, waxes, fuel oils, syngas and other useful chemical products.
To obtain petroleum fuels, waste plastics can be recycled using thermal or thermal-catalytic decomposition in an inert atmosphere. Thermal decomposition of waste plastic is enabled by shredding or thermally liquefying waste plastics and feeding the same to a reactor. The material is heated in the reactor, which results in formation of byproducts, such as, vaporized hydrocarbons and residual char. The vapors may be further reformed catalytically and are condensed to obtain fuel oils, while the char is removed from the reactor.
Primarily, there are three types of reactor designs, which are, vertical, horizontal and inclined. A vertical reactor design is provided in U.S. Pat. No. 5,584,969 (hereinafter referred to as US'969). The vertical reactor of US'969 is provided with a curved bottom end. Residue resulting from the reaction is accumulated at the center portion of the bottom surface of the reactor. The accumulated residue is removed from the reactor using suction produced by a vacuum pump. However, such vertical reactors require elaborate mechanisms for scraping of residual matter and contaminants generated during the decomposition of feedstock. Also, the use of vacuum for removing residual matter, results in loss of any useful feedstock in which the residue matter may be contained.
As recited earlier, horizontal reactors may also be used to enable thermal decomposition. Canadian Patent 1127575 discloses a horizontal reactor. The reactor is configured to receive feedstock at a first end, and at the second end, the reactor is provided with outlets for vapor and solid residue. The feedstock is conveyed from the first end towards the second end using a spiral conveyer. Since residual matter tends to stick all along the inside walls of such a conveyor, such reactors too require elaborate scraping mechanism for removal of residual matter generated during the thermal decomposition process. Such conveyors typically consist of an assembly of shafts and blades to push the feedstock towards the exit end. These shafts and blades take away valuable volumetric space which would have otherwise been available to the feedstock, thereby leading to an increase in the size of the thermal decomposition apparatus.
An adaptation of the horizontal reactor design is inclined reactor design. U.S. Pat. No. 4,094,769 discloses an inclined reactor. The reactor is configured to receive feedstock at a first end and discharge residue at a second end. The reactor is inclined in such a way that the first end is at a greater distance as compared to the second end, relative to the ground. The inclination facilitates movement of the feedstock from the first end towards the second end, due to gravity. The reactor deploys a conveyor to push the feedstock towards the exit end. Such conveyor typically consist of an assembly of shafts and blades. These shafts and blades take away valuable volumetric space which would have otherwise been available to the feedstock, thereby leading to an increase in the size of the thermal decomposition apparatus. Also, a fixed minimal gap needs to be maintained between the inside of the barrel of the conveyor and the moving blades for the conveyor to push the feedstock and any byproducts towards the exit end. Maintaining such a fixed gap may become cumbersome owing to normal wear & tear of conveyor with use.
In light of the foregoing discussion, there is a need for a technique that enables continuous removal of non-gaseous byproducts from the reactor formed during thermal or thermal-catalytic degradation process without resorting to mechanisms that comprise significantly on the volumetric space available for feedstock movement or which result in loss of useful feedstock or which require a shutdown of the process to remove the non-gaseous byproducts. The technique may enable provision of increased space for feedstock within the reactor, while enabling continuous removal of non-gaseous byproducts from the reactor. Furthermore, the technique may enable minimizing non-gaseous byproducts from accumulating in the reactors, thereby facilitating homogeneous heat transfer in the reactor and enhanced efficiency.